Power Milestones of the Future
Predicting the future is both easier and more difficult than assessing the past. Easier in that no one can say you're wrong (yet); more difficult because you don't know if you'll be right. Predicting the breakthroughs that could change the power electronics industry is doubly difficult because it is not a field that changes quickly. The loads being powered do change, but the effects on power are gradual (and often resisted). If anything, power is a "bottleneck" that can act as a constraint on application development. When something is discovered or designed that is truly enabling, the implications are significant.
Looking ahead from this point in time, four technologies could be candidates for "power milestones of the future": digital control; energy harvesting and microgenerators; high-frequency power switches; and non-silicon devices. Each of these are in research or early commercial development. All are being driven by existing applications. Some have the potential to replace current powering schemes altogether, or at least establish a competing niche. But, as befits a "projected milestone," none have revolutionized the power supply industry yet.
The technology with the greatest "breakthrough" potential is digital control. This is not a new concept, but the migration to distributed power architectures with multiple voltage rails requiring individual monitoring has made digital power management more than an expensive alternative. Energy efficiency is also driving the digital control market, as system makers demand increased performance per watt. A recent article from Ericsson indicated that "the latest mobile phones require no less than 18 voltages, often adjusted to be within a couple of millivolts. Taking into consideration that all those voltages are derived from a single voltage battery, it gives some idea of how complex energy management can be, and evidence, if it were needed, that only digital control can do the job."
Another factor that makes digital control a potential milestone is the breadth of its application. Although initially targeted at certain markets, digital power management and control is expected to be implemented in external ac-dc, embedded ac-dc, isolated dc-dc, non-isolated dc-dc (point-of-load converters and voltage regulators), telecom rectifiers, external dc-dc, and lighting ballasts. This means that early adopters will not necessarily be a dead-end niche, and will likely open the door to volume production and lower costs in other applications.
Nearly all power semiconductor companies have digital products. For example, Summit Microelectronics recently announced the SMS11, the newest device in a family of programmable monitor/sequencer/reset ICs designed for communication and consumer electronics applications.
Large-scale introduction of digitally controlled power supplies are the next step. "Darnell in Depth" reported that 18 digital converter products were introduced in 2006. Even though this is fewer than were introduced in 2005, this should change in 2007, especially for ac-dc power supplies and dc-dc converters. Several companies have said they will announce such products in 2007, with varying degrees of digital control capabilities. Such features include failure prediction and auto tuning to optimize efficiency.
Ultra-low power technologies could transform the portable device market.
Problems with batteries have driven many innovations in power electronics. Low-duty, long-life, low-cost wireless monitoring applications are now possible with IEEE 802.15.4 and ZigBee™ sensors. Long battery life allows standalone sensors to exist in many environments without wired energy sources. With millions of wireless sensors expected to be deployed in the next decade, however, replacement of millions of batteries (or entire sensor units) presents a major expense, especially for embedded sensors and sensors that are not easily accessible.
The problems with batteries are the primary driver for energy harvesting. On the one hand, many wireless sensor applications work well with batteries and are unlikely to adopt energy harvesting. As wireless sensor networks get more complex, however, the demands placed on batteries will become greater. The need to access more data, more frequently; in situ processing and analysis; hard-to-reach locations or where it would be too costly to replace large numbers of batteries; these are the situations where energy harvesting would provide value. One company said, "If anyone gets a reasonable power density from an energy harvesting device that can operate in an industrial temperature range, they will win big."
Such statements reflect the opportunity energy harvesting has to become a breakthrough technology and, potentially, a future milestone in power. Companies and research groups are still defining "energy harvesting" in different ways, however. In general, potential energy sources include light, vibration, thermal gradients, pressure differential, motion and piezoelectric (from manual depression of a push-button switch).
Advanced Linear Devices introduced a series of modules designed to capture, accumulate and store power from energy harvesting power sources and make it available for sensors, remote networks, micro machines and other applications. The modules utilize the company's patented Electrically Programmable Analog Device (EPAD) technology that allows the power generated by energy harvesting sources to go almost entirely to the application, according to the company.
Another technology that could challenge batteries is microgenerators, or microengines. Perpetuum recently launched a vibration energy harvester to power sensors, microprocessors and transmitters capable of sending large amounts of data from many types of industrial equipment. The microgenerator uses a resonant spring with coil and magnets, and a power conditioning circuit. The PMG7 is adjustable and is being used in trials. It can generate up to 5mW, and is being marketed to OEMs, sensor manufacturers and end users.
Looking further into the crystal ball, two technologies could become future power milestones. The first is a high-frequency power switch. Several companies and research labs are working on such devices. The switching losses present challenges, however, so it is uncertain whether such devices will see commercial development and adoption. The University of Toronto developed a digital controller for low-power dc-dc switchmode power supplies that allow operation at very high constant switching frequencies, up to 60MHz, suitable for portable, battery-powered systems.
Non-silicon devices are another potential milestone. Silicon nitride and silicon carbide are two such high-performance materials that could transform semiconductor fabrication and the devices used in switchmode power supplies. Cree manufactures silicon carbide-based diodes for power control and management. Cree's family of ZERO RECOVERY® rectifiers essentially has no reverse recovery at 300V, 600V and 1200V breakdown and is targeted for applications where low switching loss is required.
Because power supplies are further down the food chain, it is easy to overlook the developments that push these products forward. Most breakthroughs are still evolutionary rather than the "killer app" model of computers and communications. Ten years from now, many of today's advanced technologies will be a given; it will be interesting to see which ones truly changed the world of power supplies.
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